This invention relates to a gear pump of the type which is especially adapted to supply pressurized liquid fuel to an oil burner. The invention more particularly relates to a two-stage gear pump.
In such a gear pump, each stage comprises a spur gear secured to a drive shaft and rotatable within a ring gear. It is conventional to couple the spur gears to the shaft both with a press fit and with positive-acting keys. The keys fit into a slot formed radially through the shaft and opening axially out of the free end thereof. The slot divides the free end portion of the shaft into two cantilevered halves which are stressed and flexed toward one another when the gears are pressed onto the shaft.
A gear pump of this general type is disclosed in Harwath U.S. Pat. No. 4,728,271. In prior gear pumps, it has been necessary to form a relatively long slot in the shaft in order to relieve stress on the second stage spur gear when that gear is pressed onto the shaft. When the second stage gear is comparatively thick in an axial direction, the axial length of the slot becomes so great as to create excessively long cantilevered shaft portions. This causes manufacturing difficulties and particularly when the shaft is finished by a centerless grinding operation. Moreover, the long cantilevered shaft portions become so flexible that it is difficult to establish a tight press fit between the shaft and the first stage spur gear.